Brain May Flush Out Toxins during Sleep
TEHRAN (Tasnim) – Researchers showed for the first time that the space between brain cells may increase during sleep, allowing the brain to flush out toxins that build up during waking hours.
A good night's rest may literally clear the mind. Using mice, researchers showed that the space between brain cells may increase during sleep. These results suggest a new role for sleep in health and disease.
"Sleep changes the cellular structure of the brain. It appears to be a completely different state," Maiken Nedergaard, co-director of the Center for Translational Neuromedicine at the University of Rochester Medical Center in New York, and a leader of the study said.
For centuries, scientists and philosophers have wondered why people sleep and how it affects the brain. Only recently have scientists shown that sleep is important for storing memories. In this study, Dr. Nedergaard and her colleagues unexpectedly found that sleep may be also be the period when the brain cleanses itself of toxic molecules.
Their results, published in Science, show that during sleep a plumbing system called the glymphatic system may open, letting fluid flow rapidly through the brain. Nedergaard's lab recently discovered the glymphatic system helps control the flow of cerebrospinal fluid (CSF), a clear liquid surrounding the brain and spinal cord.
Initially the researchers studied the system by injecting dye into the CSF of mice and watching it flow through their brains while simultaneously monitoring electrical brain activity. The dye flowed rapidly when the mice were unconscious, either asleep or anesthetized. In contrast, the dye barely flowed when the same mice were awake.
"We were surprised by how little flow there was into the brain when the mice were awake," said Dr. Nedergaard. "It suggested that the space between brain cells changed greatly between conscious and unconscious states."
To test this idea, the researchers used electrodes inserted into the brain to directly measure the space between brain cells. They found that the space inside the brains increased by 60 percent when the mice were asleep or anesthetized.
Certain brain cells, called glia, control flow through the glymphatic system by shrinking or swelling. Noradrenaline is an arousing hormone that is also known to control cell volume. Similar to using anesthesia, treating awake mice with drugs that block noradrenaline induced unconsciousness and increased brain fluid flow and the space between cells, further supporting the link between the glymphatic system and consciousness.
The results may also highlight the importance of sleep.
"We need sleep. It cleans up the brain," Dr. Nedergaard pointed out.